Transfer credit from existing subscription

I've recently changed from a first Gen Ring to the 2020 Ring 2, and have been automatically given a free protect trial. I had an annual subscription for my previous device, which does not expire until Jan 27th. How do I replace my old device with my new one, on my current subscription. I spoke to one of your call takers, who had no clue, and simply told me to call back when my trial period ends.